THE EFFECT OF DIFFUSE FUNCTIONS ON MINIMAL BASIS SET SUPERPOSITION ERRORS FOR H-BONDED DIMERS

The effect of the addition of diffuse functions of sp type on the first row atoms (and/or of d type on phosphorus) to a MINI‐1 minimal basis set is evaluated by comparing the SCF description of the interaction energy and its decomposition, counterpoise (CP) corrected and uncorrected for basis set superposition errors (BSSEs), with that produced by extended basis sets (6‐31G** and 3‐21G+) as well as by basis sets (6‐31G** + VPS and (2d)S), previously successfully tested, designed to minimize the BSSE. The systems considered are a few anions (F−, HCOO−, H2PO−4) H‐bonded to water; the basis set performance on a different geometry (bifurcated instead of linear) of the phosphate‐water adduct was also considered. An additional comparison with the interaction energy in a neutral dimer, (HF)2, was carried out. The addition of diffuse functions to the MINI‐1 basis set, instead of resorting to extended basis sets, seems to be a sensible choice for anions. The equilibrium distance is shifted towards the reference basis set value at the CP corrected level as well as at the uncorrected one. The spread of the energy due to the basis set is hardly distinguishable when the CP corrected values are plotted. The description of the interaction energy in dimers involving phosphorus is improved using d type diffuse functions. Copyright © 1990 John Wiley & Sons, Inc.